1. Technical Field
The invention relates in general to a receiver.
2. Background
A concern when designing radio frequency (RF) receivers for wireless communication systems is to detect a relatively weak in-band signal in the presence of a strong out-of-band jammer. If the linearity of the receiver is insufficient, such jammer may saturate the receiver and block the in-band signal. Using a surface acoustic wave (SAW) filter in front of the receiver is the most common solution to this problem. The SAW filter has band-pass capability with a very high quality (Q) factor, thereby capable of providing a large rejection ratio to the out-of-band jammer (normally greater than 20 dB) and meeting the receiver linearity requirement.
However, in-band attenuation of the SAW filter tends to make it harder to detect weak signals, creating the need for an even more sensitive receiver after the SAW filter. In addition, there is currently no economical way to implement SAW filters or their equivalents in the same processes as the active circuits that follow them, which are typically produced using CMOS or BiCMOS processes and either silicon or silicon germanium technologies. Therefore, SAW filters usually have to be purchased additionally and significantly increase the cost and consume equally valuable circuit board area in a typical communication device. The above problems are further exacerbated by the proliferation of different frequency bands that a communication device has to be compatible with.